A. Technical Field
The present invention relates to systems, devices, and methods of managing traffic in communication systems, and more particularly, to the optimization of data transfer rates between Serial Attached SCSI devices.
B. Background of the Invention
There is growing demand for deploying Serial-Attached-SCSI (SAS) topologies in tiered storage environments that use different types of storage devices with incongruous performance attributes. For example, Solid State Disk drives (SSDs) provide substantially higher random I/O performance compared with their mechanical counterparts in exchange for a much higher dollar-per-gigabyte price point. It is increasingly popular to have systems utilizing a number of SSDs for their significantly faster access rate alongside a much larger number of slower, inexpensive mechanical spinning disk drives. This combination of different types of devices within a storage network presents unique challenges.
The SAS signaling protocol includes standard fairness rules intended to provide fair access to all devices equally, which comes at the expense of reducing the performance of ultra high performance devices, such as SSDs, that did not exist when the SAS fairness rules were designed. As a result, when system designers use high performance devices together with significantly slower devices in SAS storage systems, the standard fairness protocol causes underutilization of the ultra fast devices that have to share data bandwidth with all the slower devices.
What is needed are tools for system designers to overcome the above-described limitations.